Recently, various electronic devices, especially mobile terminals, such as potable phones, have included light emitting diodes or electroluminescence elements for illuminating operating sections so that push buttons or display sheets can be easily operated and identified even when it is dark around the devices. Movable contact assemblies and switches used in these devices are required to be inexpensive and allow various illuminations.
FIG. 7 is a sectional view of conventional movable contact assembly 4. Light guiding sheet 1 having a film shape is light-transmittable and has flexibility. Diffusing portions 1A are formed on an upper surface of light guiding sheet 1. Light guiding sheet 1 has a predetermined portion of a periphery attached with adhesive onto cover sheet 2 having a film shape.
Movable contact 3 is made of thin plate of conductive metal having a substantially dome shape. Plural Movable contacts 3 are attached onto a lower surface of cover sheet 2 under diffusion portions 1A with an adhesive, thus providing movable contact assembly 4.
FIG. 8 is a sectional view of conventional switch 501. Wiring board 5 has wiring patterns on upper and lower surfaces thereof. Fixed contacts 6 including center fixed contacts 6A and outer fixed contacts 6B are provide on an upper surface of wiring board 5. Each center fixed contact 6A has a substantially circular shape. Each outer fixed contact 6B has a substantially horseshoe shape or a substantially ring shape that surrounds center fixed contact 6A.
Movable contact assembly 4 is attached onto the upper surface of wiring board 5. An outer periphery of movable contact 3 is mounted onto outer fixed contact 6B. The center of a lower surface of movable contact 3 faces center fixed contact 6A with a predetermined gap.
Light emitting element 7, such a light emitting diode, is mounted onto the upper surface of wiring board 5 and at the right side of light guiding sheet 1. Light emitting element 7 has a light emitting surface facing right edge surface 1C of light guiding sheet 1.
Actuator 8 made of insulating resin includes is formed of light-transmittable portion 8A and light-blocking portion 8B covering an upper surface of actuator 8. Display portion 8C including exposing light-transmittable portion 8A exposed in a shape of characters or symbols is provided on the upper surface of actuator 8. Pressing portion 8D projecting downward from actuator 8 contacts the upper surface of light guiding sheet 1 above the center of movable contact 3.
Movable contact assembly 4 and wiring board 5 are accommodated in case 9 made of insulating resin having a substantially box shape. Actuator 8 is vertically movably mounted in an opening provided in an upper surface of case 9, thus providing switch 501.
Switch 501 is mounted to an operation panel of an electronic device. Center fixed contacts 6A, outer fixed contacts 6B, and light emitting element 7 are connected to an electronic circuit of the electronic device via the wiring patterns.
When actuator 8 is pressed down, pressing portion 8D on the lower surface of actuator 9 presses light guiding sheet 1, and light guiding sheet 1 and cover sheet 2 bend accordingly, thereby applying a pressing force to the center of the substantially dome shape of movable contact 3. When the pressing force exceeds a predetermined value, movable contact 3 has its shape elastically reversed downward with a click feeling, and the center of the lower surface of movable contact 3 contacts center fixed contact 6A. Thereby, center fixed contact 6A is electrically connected to outer fixed contact 6B via movable contact 3.
When the pressing force to actuator 8 is released, movable contact 3 has its shape elastically reversed upward by an elastic restoring force, the center of the lower surface of movable contact 3 is removed from center fixed contact 6A, thereby disconnecting center fixed contact 6A electrically from outer fixed contact 6B.
According to the electrical connection and disconnection between fixed contacts 6A and 6B, the electronic circuit switches functions of the electronic device.
The electronic circuit applies a voltage is applied to light emitting element 7 to generate light LL. Light LL is introduced from right edge surface 1C into light guiding sheet 1, and travels left in light guiding sheet 1 while being reflected on surfaces of the light guiding sheet. This light is diffused by diffusing portions 1A on the upper surface of light guiding sheet 1, and illuminates display portion 8C of actuator 8 from beneath. Even in dark environment, a user can identify the characters or symbols of display portion 8C, and easily operate the electronic device.
In switch 501 including movable contact assembly 4, the light from light emitting element 7 is guided into light guiding sheet 1 from the edge surface perpendicular to the light. When light guiding sheet 1 is thin, a sufficient amount of light cannot be guided into light guiding sheet 1, light from diffusing portions 1A becomes weak, accordingly preventing display portion 8C from being illuminated brightly.